Electrostatic developing apparatus



Sept. 5, 1961 G. A. HARRIS ETAL 2,998,802

ELECTROSTATIC DEVELOPING APPARATUS Filed Jan. 2s, 1G59 ...W vf

`27 74/\ F f9.3 u 21 23 51* 5 JNVENToRs 2 G GEORGE A. HARms "\\`$1 BY ELGOD I MONTGOMERY 8 0 I V832 AGENT United States Patent O 2,998,802ELECI'ROSTATIC DEVELOPING APPARATUS George A. Harris, Malvern, andElwood T. Montgomery, Drexel Hill, Pa., assignors to BurroughsCorporation, Detroit, Mich., a corporation of Michigan Filed Jau. 28,1959, Ser. No. 789,725 6 Claims. (Cl. 118-637) The invention hereinafterdescribed and claimed has to do with electrostatic apparatus and moreparticularly to apparatus for visibly developing informationelectrostatically recorded on a recording medium.

The electrostatic recording process consists broadly of three steps. Thefirst step comprises establishing, or printing, electrically chargedareas on selected portions of a recording medium, which arerepresentative of information. The second step consists of developingsuch charged areas on the recording medium by means of an inking powderthus to make them visible. The third step, which is optional, consistsin xing, or rendering such developed areas substantially permanent. Inthe electrostatic recording process, these three steps take placesequentially and at physically separate locations.

The recording medium is preferably made of a backing layer, or web ofpaper, on one side of which is bonded a thin layer of high resistivity,or dielectric material. The web of paper is moved through the printingapparatus where the electrostatically charged areas are established andfrom this station it passes to the inking and fixing stationssequentially.

During the developing or inking of the latent electrostatic image,developing powder or ink will adhere to the electrostatically chargedareas, thus to make them visible. Unfortunately under some conditionspowder will also adhere to the background or uncharged portions of therecording material. This is au undersirable condition as it tends toobscure the desired information.

Therefore, it is an important object of the present invention to providenovel apparatus for developing or inking electrostatically recordedinformation or images in a manner overcoming this disadvantage.

More specifically, it is an object of the present invention to provide anovel inking device for images electrostatically recorded on a recordmedium whereby ink adhering to the uncharged or background areas of therecording medium is removed.

Another object of the invention is to provide such apparatus which willrecover Ithe ink removed from the noncharged or background areas of therecording medium.

ln accordance with the above objects and first briefly described, theinvention comprises apparatus through which an electrostatically chargedweb of recording material may be passed for developing the charged areaswith inking powder which is maintained in contact with the charged sideof the web. The inking powder is housed in a chamber including suctioncleaning apparatus for causing air to sweep across the inked surfacethus to remove excess ink which is returned to the ink supply.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered with theaccompanying drawings wherein:

FIG. l is a perspective view of apparatus embodying the invention, withparts removed better to show the interior of the apparatus;

FIG. 2 is a sectional view of the apparatus, taken along line 2-2 ofFIG. 3; and

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.

Referring now to the drawing illustrating the preferred form of theinvention, and first to FIGS. 1 and 3, it will be seen that theapparatus comprises a housing 10, somewhat triangular in cross-section,and formed by a bottom wall 11, a back wall 12, a top Wall 13, sidewalls 14, and a front wall 15. The forward or right hand ends of bottomand top walls 11 and 13 terminate short of front wall 15 thus to providean inlet opening or slot 16 and an outlet opening or slot 17respectively, both of which extend across the housing to points adjacentthe side walls 14, and together provide means whereby a record mediummay be threaded through the housing. While other types of record mediummay be used, in the presently described embodiment of the invention itis a web of paper 18 of the type described above. It will be understoodthat the web of paper may be fed through the housing continuously orincrementally step-by-step, by means not shown. In the latter case thespeed may be such that it can be described as being substantiallyconstant.

Front wall 15 is provided with a curved inner surface 19 over which theweb 18 is tightly held as it is fed through the chamber 20 enclosed bythe housing 10. Feeding of the web may be by any suitable well knownmeans, such as rollers, not shown.

A strip of exible material 21, such as felt, is secured by suitablemeans, along the front edge of bottom Wall 11. The forward edge 22 ofthe felt member is turned upwardly and maintained flexed against the web18, or wall 15 if no web is present, by a spring leaf 23 also suitablysecured to the front edge of bootom wall 11 and terminating adjacent thefront edge of the felt member 21. lnlet opening 16 thus is sealed in amanner preventing ink from spilling out of the housing.

With reference to FIGURES 1 and 2, it will be seen that the upperportion of curved surface 19 of front wall 15 is spanned by the inkremoving apparatus indicated generally by the numeral 24 and securedupon spaced abutments 25, projecting from surface 19, as by screws 26,thus to provide a slot 27 through which web 18 is threaded.

The ink removing device is a suction cleaner formed by a plurality ofelongated members 32, 33, 34, 35, 36 and 37 secured together in stackedrelationship, as by screws 38. Member 32 is formed with a pair ofaligned elongated recesses 39 and 39a in its upper face, as seen in FIG.2, which are enclosed by member 33 to form a pair of aligned elongatedchambers 40 and 40a. A pair of aligned recesses or chambers 41 and 41ain the outer or curved right hand face 42 of member 32 (FIG. 3) are inopen communication with chambers 40 and 40a respectively as by apertures43a spaced along the length of wall 43 separating the chambers. The wall41h separating chamber 41 and 41a is tapered to a thin leading edgefacing web 18 so as not to block air from sweeping over this portion ofthe web. Member 33 is formed with two spaced recesses 44 and 45 whichare formed into elongated chambers 46 and 47 by plate members 34 and 36respectively, which chambers are in communication with chambers 40 and40a as by apertures 48 and 49 respectively. Valves 50 and 51 normallymaintain apertures 48 and 49 in closed condition, but are responsive tolow pressure in chambers 46 and 47 to open the apertures.

`Chamber 46 is in open communication with one chamber 52 of a diaphragmpump 53 by means of pipe 54 and conduit 55, the latter being formed byaligned holes through wall 15 and members 32 land 33. In like manner,chamber 47 at the right hand side of the ink removing device, isconnected to chamber 56 of pump 53 by pipe 57 and conduit 58, the latterbeing `formed in the same manner as conduit `55 on the left hand side ofthe apparatus.

Members 35 and 37 `are 4formed with recesses 59 and 60 respectively ontheir undersides, as seen in FIGURE 2, and cooperate with plates 34 yand36 to `form conduits 61 and 62 which communicate with chambers 46 and 47by means of apertures 63 and 64 respectively. the latter being normallyclosed by pressure responsive valves 65 and `66. The outlet ends 67 and68 of these conduits are in open communication with `housing chamber 20containing ia supply of ink 69.

Pump S3 may be of any suitable kind but for the purpose of illustration.is shown asbeing of the type wherein a flexible diaphragm 70 serves bothas the pumping or air displacing means, and the means for dividing thepump housing into the two chambers 52 and 56 mentioned above, therebyeffecting double action for each pump cycle, as described below. Thediaphragm is normally urged to the left. as seen in FIGURE 2, by coilspring 72 positioned on one side thereof, and is provided on its otherside with an actuating rod 73 which extends through the wall 74 into thepath of rotation of a cam 75 mounted on a shaft 76 driven by a motor 77.

In the operation of the apparatus, motor 77 is energized by suitablemeans, not shown, to rotate cam 75. During the iirst half-rotation ofthe cam to the broken line position 78a. its high point 78 will move rod73, and diaphragm 70 to the right, as seen in FIGURE 2, to the lbrokenline position 70a against the pressure of coil spring 72. Continuedrotation returns the cam to `its full line position whereby spring 72 iseffective to return the diaphragm to its full line position as the endof rod 73 follows the periphery of cam 75 to its low point. It is seen,therefore, that each reciprocatory cycle of plunger 73 and consequentlydiaphragm 70 effect both a pressure and a sucking action through pipes54 and 57 and their associated conduits and chambers, as more fullydescribed below.

Considering first the movement of diaphragm 70 from its full lineposition to its broken line position. as illustrated in FIG. 2, air willbe displaced from chamber 56 and forced through pipe 57, conduit 58 andinto chamber '47. causing valve 51 to close aperture 49 and valve 66 toopen aperture 64 permitting the high pressure air to ow through theaperture into conduit 62 and through outlet opening 68 into housing 20.Simultaneously the chamber 52 of the pump is enlarged, creating a lowpressure in this chamber causing air to be sucked through pipe 54,conduit 55 and chamber 46, thus to reduce the pressure in the latterchamber. In response to this lowered pressure in chamber 46 valve 65closes aperture 63 |and valve 50 opens aperture 48. Chamber 40 thus isopened to the sucking action of. the pump causing air to be sucked athigh velocity from chamber 20 to sweep through the left hand half ofslot 27 through chamber 41. apertures 43a. chamber 40. aperture 48. intochamber 46, conduit 55, pipe 54 and pump chamber 52.

On its retum stroke to the full line position the abovedescribed pumpingaction is reversed. Chamber 52 becomes the high pressure side andchamber 56 the low pressure side. 'From chamber 52 air is forced throughpipe 54. conduit 55. chamber 46. aperture 63 (valve 65 being opened andvalve 58 closed by the pressure difr["erential across them), conduit 61,and through outlet 67 into housing chamber 20. The low pressure createdin chamber 56 by this stroke of diaphragm 70 sucks air into the chamberthrough pipe 57. conduit 58, chamber 47, aperture 49 (valve 66 beingclosed and valve 51 opened by the pressure differential across them) toreduce the pressure in chamber 40a. Thus air from housing chamber 20 iscaused to sweep at high velocity through the right hand half of slot 27,through chamber 41a, apertures 43a, chamber 40a, aperture 49, and intochamber 47, conduit 58. pipe 57 and pump chamber 56. Thus it is seenthat each complete cycle of pump 53 effects a sweep of air from chamber20 at high velocity through the full width of slot 27, and the return ofthe air to chamber 20.

Web 18 previously fed through inlet opening 16, slot 27 and out of thehousing through slot 17 is drawn tightly against curved surface 19offront wall 15,` as it moves through the apparatus, either continuouslyor incrementally as described' above. Information is electrostaticallycharged or printed on the web by the apparatus shown at 80, whichincludes at least one, but preferably a row ofv printing heads 81, asseen in FIG. 1, and a back-up electrode 82, all in accordance with thelapparatus described in the copending application of Epstein et al.,Serialv No. 714,767, filed February l2, 1958, and assigned to theassignee of the present invention. Incidentally, a suitable ink for usein the apparatus is also described in this copending application.

As the charged paper moves through the lower portion of the housing, inkparticles adhere to the latent image on the charged portion of web 18',thus visibly developing these images. Unfortunately, as mentioned above,some of the ink Imay also adhere to the background or uncharged areas ofthe web. However, in particular accordance with the present invention,as the web passes through slot 27, the high velocity air passing throughthe slot, as described above, sweeps across the paper yand forciblyremoves the unwanted ink adhering to the web. The ink entrained in theiair on the suction stroke of the pump is returned to lhousing chamber20 on the pressure stroke.

To facilitate inking of the web, van ink agitator is positioned in theink supply 69. The agitator is rotated by its mounting shaft 86 in acounterclockwise direction whereby its agitator vanes 87 urge theparticles of ink toward the web as it passes through the housing.Rotation of the agitator 85 may be effected in any convenient mannersuch as by the pulley 88 secured to the end of shaft 86 and driven ybybelt 89 shown in FIG. l, it being understood, of course, that belt 89can be driven by any well known means, not shown, `but which may bemotor 77, if desired.

Thus it is seen that the invention provides apparatus which will developa clean copy of information electrostatically recorded on the web 18,and iat the same time recover the excess ink removed from the web.

We claim:

l. Apparatus for visibly developing images electrostatically recorded onone side of a recording medium comprising, a housing for holding asupply of inking powder. said housing having inlet and outlet openingsthrough which said record medium may be passed through said housing, theelectrostatically charged side of said record ing medium being incontact with said inking powder as the record medium passes through saidhousing thus to develop the images recorded thereon, suction cleaningmeans within said housing, said suction cleaning means including achamber having an opening extending across and closely adjacent saiddeveloped surface of said record medium, means for reducing the pressurewithin said chamber whereby air is drawn from within said housing tosweep across said developed surface of said record medium and into saidchamber, thereby to remove excess ink from said record medium, and meansfor exhausting the air and the excess ink from said chamber into saidhousing.

2. A construction according to claim l wherein said pressure reducingmeans includes a pump, means between said pump and said chamberpermitting said pump on its suction stroke to draw air from said chamberthus to reduce the pressure therein, but preventing air from enteringsaid chamber on the pressure stroke of said pump, and means effective todischarge air from said pump into said housing on said pressure strokeof said pump.

3. A construction in accordance with claim 1 wherein said pressurereducing means includes a pump, conduit means connecting said pump tosaid chamber, first valve means between said conduit and said chamberpermitting said pump on its suction stroke to draw air from said chamberthus to reduce the pressure therein, but preventing air from enteringsaid chamber from said conduit on the pressure stroke of said pump, andsecond valve means in said conduit effective to discharge air from saidconduit into said housing on said pressure stroke of said pump.

4. A construction according to claim 3 and including a second chamberaligned with said first mentioned chamber and separated therefrom hy amedial wall, said combined chambers spanning said record medium, andwherein said conduit means includes first and second conduits, eachconduit including first and second valve means, and said pump includesfirst and second ports each alternating as suction and pressure ports,said first conduit connecting said first mentioned chamber to said firstport, and said second conduit connecting said second chamber to saidsecond port, whereby each cycle of said pump effects both a suction anda pressure condition through its associated conduits alternately toremove air from said chambers and move it into said housing.

5. Apparatus for visibly developing images electrostatically recorded onone side of a recording medium comprising, a housing for holding asupply of inking powder, said housing having inlet and outlet openingsthrough which said record medium may be passed through said housing, theelectrostatically charged side of said recording medium being in contactwith said inking powder as the record medium passes through said housingthus to develop the images recorded thereon, suction cleaning meanswithin said housing, said housing including a wall over which saidrecord medium moves during its passage through said housing, saidsuction cleaning means including an elongated member with one faceclosely adajacent said wall thereby to form a narrow slot through whichsaid record medium moves in passing through said housing, a pair ofaligned recesses in said one face of said member forming chamberstherein, said chambers facing said wall and each Spanning approximatelyone half the Width of said record medium, and means alternately toreduce the pressure within said chambers thus to cause housing air tosweep through said slot at high velocity and across said record medium,first across the half spanned by one of said chambers and then the halfspanned by the other of said compartments, thus to remove excess inkfrom the developed surface of said record medium.

6. Apparatus in accordance with claim 5 wherein said last means includesa pump having first and second ports each alternating as suction andpressure ports on each cycle of said pump, and conduit means connectingone of said ports to one of said chambers and to the interior of saidhousing, and the other of said ports to the other of said chambers andto the interior of said housing, and valve means in said conduitseffective to open said conduits to said chambers only on the suctionstroke of said pump relative to a given port, and to the interior ofsaid housing only on the pressure stroke of said pump relative to agiven port.

References Cited in the file of this patent UNITED STATES PATENTS2,732,775 Young et al. Jan. 31, 1956 2,842,456 Carlson July 8, 19582,851,373 Tregay et al. Sept. 9, 1958 2,862,472 Carlson Dec. 2, 19582,892,446 Olden June 30, 1959

